ALTER SESSION SET TIME_ZONE = '-5:0';
SELECT SESSIONTIMEZONE, CURRENT_DATE FROM DUAL;

SESSIONTIMEZONE CURRENT_DATE
 --------------- --------------------
 
- 05 : 00            21 . 02 . 2003   13 : 14 : 03 

ALTER SESSION SET TIME_ZONE = '-8:0';
SELECT SESSIONTIMEZONE, CURRENT_DATE FROM DUAL;

SESSIONTIMEZONE CURRENT_DATE
 --------------- --------------------
 
- 08 : 00            21 . 02 . 2003   10 : 14 : 33 

CURRENT_DATE RETURN DATE
CURRENT_TIMESTAMP RETURN TIMESTAMP_TZ_UNCONSTRAINED
LOCALTIMESTAMP RETURN TIMESTAMP_UNCONSTRAINED
SYSDATE RETURN DATE
SYSTIMESTAMP RETURN TIMESTAMP_TZ_UNCONSTRAINED